Measuring large lipid droplet sizes by probing restricted lipid diffusion effects with diffusion-weighted MRS at 3T.

PURPOSE: The in vivo probing of restricted diffusion effects in large lipid droplets on a clinical MR scanner remains a major challenge due to the need for high b-values and long diffusion times. This work proposes a methodology to probe mean lipid droplet sizes using diffusion-weighted MRS (DW-MRS) at 3T. METHODS: An analytical expression for restricted diffusion was used. Simulations were performed to evaluate the noise performance and the influence of particle size distribution. To validate the method, oil-in-water emulsions were prepared and examined using DW-MRS, laser deflection and light microscopy. The tibia bone marrow was scanned in volunteers to test the method repeatability and characterize microstructural differences at different locations. RESULTS: The simulations showed accurate and precise droplet size estimation when a sufficient SNR is reached with minor dependence on the size distribution. In phantoms, a good correlation between the measured droplet sizes by DW-MRS and by laser deflection (R2 = 0.98; P = 0.01) and microscopy (R2 = 0.99; P < 0.01) measurements was obtained. A mean coefficient of variation of 11.5 % was found for the lipid droplet diameter in vivo. The average diameter was smaller at a proximal (50.1 ± 7.3 µm) compared with a distal tibia location (61.1 ± 6.8 µm) (P < 0.01). CONCLUSION: The presented methods were able to probe restricted diffusion effects in lipid droplets using DW-MRS and to estimate lipid droplet size. The methodology was validated using phantoms and the in vivo feasibility in bone marrow was shown based on a good repeatability and findings in agreement with literature.

Differentiating supraclavicular from gluteal adipose tissue based on simultaneous PDFF and T2 * mapping using a 20-echo gradient-echo acquisition.

BACKGROUND: Adipose tissue (AT) can be classified into white and brown/beige subtypes. Chemical shift encoding-based water-fat MRI-techniques allowing simultaneous mapping of proton density fat fraction (PDFF) and T2 * result in a lower PDFF and a shorter T2 * in brown compared with white AT. However, AT T2 * values vary widely in the literature and are primarily based on 6-echo data. Increasing the number of echoes in a multiecho gradient-echo acquisition is expected to increase the precision of AT T2 * mapping. PURPOSE: 1) To mitigate issues of current T2 *-measurement techniques through experimental design, and 2) to investigate gluteal and supraclavicular AT T2 * and PDFF and their relationship using a 20-echo gradient-echo acquisition. STUDY TYPE: Prospective. SUBJECTS: Twenty-one healthy subjects. FIELD STRENGTH/SEQUENCE ASSESSMENT: First, a ground truth signal evolution was simulated from a single-T2 * water-fat model. Second, a time-interleaved 20-echo gradient-echo sequence with monopolar gradients of neck and abdomen/pelvis at 3 T was performed in vivo to determine supraclavicular and gluteal PDFF and T2 *. Complex-based water-fat separation was performed for the first 6 echoes and the full 20 echoes. AT depots were segmented. STATISTICAL TESTS: Mann-Whitney test, Wilcoxon signed-rank test and simple linear regression analysis. RESULTS: Both PDFF and T2 * differed significantly between supraclavicular and gluteal AT with 6 and 20 echoes (PDFF: P < 0.0001 each, T2 *: P = 0.03 / P < 0.0001 for 6/20 echoes). 6-echo T2 * demonstrated higher standard deviations and broader ranges than 20-echo T2 *. Regression analyses revealed a strong relationship between PDFF and T2 * values per AT compartment (R2 = 0.63 supraclavicular, R2 = 0.86 gluteal, P < 0.0001 each). DATA CONCLUSION: The present findings suggest that an increase in the number of sampled echoes beyond 6 does not affect AT PDFF quantification, whereas AT T2 * is considerably affected. Thus, a 20-echo gradient-echo acquisition enables a multiparametric analysis of both AT PDFF and T2 * and may therefore improve MR-based differentiation between white and brown fat. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:424-434.

Milk cloud appearance-a characteristic sign of fibrous dysplasia on contrast-enhanced MR imaging.

OBJECTIVE: To evaluate contrast-enhanced T1-weighted magnetic resonance (MR) images in histologically proven fibrous dysplasia (FD) for the prevalence of "milk cloud appearance" and its association with ground-glass appearance (GGA) on radiography or computed tomography (CT). METHODS: For this retrospective cohort study, 37 patients with histologically proven FD imaged preoperatively with contrast-enhanced MR imaging and radiography or CT were identified at our institution. Three radiologists independently evaluated MR images for the presence of milk cloud appearance on T1-weighted contrast-enhanced images, sites of skeletal involvement, type of bone involved, uni- vs. multifocality, mono- vs. polyostotic disease, maximum diameter, proportion of bone involved, expansile remodeling, and T2 homogeneity. The presence or absence of GGA on radiography or CT was determined in consensus. Inter-reader agreement was evaluated for milk cloud appearance using Cohen's kappa, and associations between milk cloud appearance and other imaging parameters were tested using Spearman's rho. RESULTS: Among the 37 histologically proven FD lesions, GGA was identified in 70% of the lesions, while milk cloud appearance was found in 82% of the lesions. Inter-reader agreement for milk cloud appearance on MR imaging was good to excellent (κ 0.65, 0.82, and 0.8). A significant correlation was found between milk cloud appearance and GGA (ρ = 0.31, p < 0.001). CONCLUSION: Milk cloud appearance is a characteristic sign of FD on contrast-enhanced T1-weighted MR images. Recognition of this feature may be helpful when radiographs are equivocal or unremarkable or when MR imaging is performed as the primary imaging modality in cases of FD. KEY POINTS: • Fibrous dysplasia displays a characteristic feature on contrast-enhanced T1-weighted MR imaging: milk cloud appearance. • Milk cloud appearance correlates well with the radiographic or CT finding of ground-glass appearance. • Recognition of milk cloud appearance on contrast-enhanced MR imaging may be helpful when radiographs are equivocal or unremarkable or when MR imaging is performed as the primary imaging modality in cases of fibrous dysplasia.

Techniques and Applications of Magnetic Resonance Imaging for Studying Brown Adipose Tissue Morphometry and Function.

The present review reports on the current knowledge and recent findings in magnetic resonance imaging (MRI) and spectroscopy (MRS) of brown adipose tissue (BAT). The work summarizes the features and mechanisms that allow MRI to differentiate BAT from white adipose tissue (WAT) by making use of their distinct morphological appearance and the functional characteristics of BAT. MR is a versatile imaging modality with multiple contrast mechanisms as potential candidates in the study of BAT, targeting properties of 1H, 13C, or 129Xe nuclei. Techniques for assessing BAT morphometry based on fat fraction and markers of BAT microstructure, including intermolecular quantum coherence and diffusion imaging, are first described. Techniques for assessing BAT function based on the measurement of BAT metabolic activity, perfusion, oxygenation, and temperature are then presented. The application of the above methods in studies of BAT in animals and humans is described, and future directions in MR study of BAT are finally discussed.

Quantitative MRI and spectroscopy of bone marrow.

Bone marrow is one of the largest organs in the human body, enclosing adipocytes, hematopoietic stem cells, which are responsible for blood cell production, and mesenchymal stem cells, which are responsible for the production of adipocytes and bone cells. Magnetic resonance imaging (MRI) is the ideal imaging modality to monitor bone marrow changes in healthy and pathological states, thanks to its inherent rich soft-tissue contrast. Quantitative bone marrow MRI and magnetic resonance spectroscopy (MRS) techniques have been also developed in order to quantify changes in bone marrow water-fat composition, cellularity and perfusion in different pathologies, and to assist in understanding the role of bone marrow in the pathophysiology of systemic diseases (e.g. osteoporosis). The present review summarizes a large selection of studies published until March 2017 in proton-based quantitative MRI and MRS of bone marrow. Some basic knowledge about bone marrow anatomy and physiology is first reviewed. The most important technical aspects of quantitative MR methods measuring bone marrow water-fat composition, fatty acid composition, perfusion, and diffusion are then described. Finally, previous MR studies are reviewed on the application of quantitative MR techniques in both healthy aging and diseased bone marrow affected by osteoporosis, fractures, metabolic diseases, multiple myeloma, and bone metastases. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:332-353.

Evaluation of an iterative model-based CT reconstruction algorithm by intra-patient comparison of standard and ultra-low-dose examinations.

Background The explosive growth of computer tomography (CT) has led to a growing public health concern about patient and population radiation dose. A recently introduced technique for dose reduction, which can be combined with tube-current modulation, over-beam reduction, and organ-specific dose reduction, is iterative reconstruction (IR). Purpose To evaluate the quality, at different radiation dose levels, of three reconstruction algorithms for diagnostics of patients with proven liver metastases under tumor follow-up. Material and Methods A total of 40 thorax-abdomen-pelvis CT examinations acquired from 20 patients in a tumor follow-up were included. All patients were imaged using the standard-dose and a specific low-dose CT protocol. Reconstructed slices were generated by using three different reconstruction algorithms: a classical filtered back projection (FBP); a first-generation iterative noise-reduction algorithm (iDose4); and a next generation model-based IR algorithm (IMR). Results The overall detection of liver lesions tended to be higher with the IMR algorithm than with FBP or iDose4. The IMR dataset at standard dose yielded the highest overall detectability, while the low-dose FBP dataset showed the lowest detectability. For the low-dose protocols, a significantly improved detectability of the liver lesion can be reported compared to FBP or iDose4 ( P = 0.01). The radiation dose decreased by an approximate factor of 5 between the standard-dose and the low-dose protocol. Conclusion The latest generation of IR algorithms significantly improved the diagnostic image quality and provided virtually noise-free images for ultra-low-dose CT imaging.

Using simulated fluorescence cell micrographs for the evaluation of cell image segmentation algorithms.

BACKGROUND: Manual assessment and evaluation of fluorescent micrograph cell experiments is time-consuming and tedious. Automated segmentation pipelines can ensure efficient and reproducible evaluation and analysis with constant high quality for all images of an experiment. Such cell segmentation approaches are usually validated and rated in comparison to manually annotated micrographs. Nevertheless, manual annotations are prone to errors and display inter- and intra-observer variability which influence the validation results of automated cell segmentation pipelines. RESULTS: We present a new approach to simulate fluorescent cell micrographs that provides an objective ground truth for the validation of cell segmentation methods. The cell simulation was evaluated twofold: (1) An expert observer study shows that the proposed approach generates realistic fluorescent cell micrograph simulations. (2) An automated segmentation pipeline on the simulated fluorescent cell micrographs reproduces segmentation performances of that pipeline on real fluorescent cell micrographs. CONCLUSION: The proposed simulation approach produces realistic fluorescent cell micrographs with corresponding ground truth. The simulated data is suited to evaluate image segmentation pipelines more efficiently and reproducibly than it is possible on manually annotated real micrographs.

An observational, prospective study to evaluate the preoperative planning tool "CI-Wizard" for cochlear implant surgery.

"CI-Wizard" is a new, three-dimensional software planning tool for cochlear implant surgery with manual and semi-automatic algorithms to visualize anatomical risk structures of the lateral skull base preoperatively. Primary endpoints of the study represented the evaluation of the CI-Wizards usability, accuracy, subjectively perceived and objectively measured time in clinical practice. In a period from January 2014 to March 2015, n = 36 participants were included in this study. These members were divided into three groups of equal number (n = 12), but different level of experience. Senior doctors and consultants (group 1), residents (group 2) and medical students (group 3) segmented 12 different CT-scan data sets of the CI-Wizard (four per participant). In total, n = 144 data sets were collected. The usability of the CI-Wizard was measured by the given questionnaire with an interval rating scale. The Jaccard coefficient (JT) was used to evaluate the accuracy of the anatomical structures segmented. The subjectively perceived time was measured with an interval rating scale in the questionnaire and was compared with the objectively mean measured time (time interact). Across all three groups, the usability of the CI-Wizard has been assessed between 1 ("very good") and 2 ("with small defects"). Subjectively, the time was stated as "appropriate" by questionnaire. Objective measurements of the required duration revealed averages of t = 9.8 min for creating a target view. Concerning the accuracy, semi-automatic anatomical structures such as the external acoustic canal (JT = 0.90), the tympanic cavity (JT = 0.87), the ossicles (JT = 0.63), the cochlea (JT = 0.66), and the semicircular canals (JT = 0.61) reached high Jaccard values, which describes a great match of the segmented structures between the partcipants and the gold standard. Facial nerve (JT = 0.39) and round window (JT = 0.37) reached lower Jaccard values. Very little overlap tendency was found for the chorda tympani (JT = 0.11). This software program represents a further important step in the development of preoperative planning tools in cochlear implant surgery. The study revealed a high level of satisfaction in the usability. The subjectively required time was considered as "appropriate" and the objectively mean measured time was t = 9.8 min short enough, so that a clinical application seems realistic. Particularly for semi-automatically segmented structures, it represented a good accuracy. For purely manual segmented structures, further improvements are desirable. Finally, this program also provides a good learning tool for medical students and residents to become familiar with the anatomy of the lateral skull base.

Assessment of paraspinal muscle characteristics, lumbar BMD, and their associations in routine multi-detector CT of patients with and without osteoporotic vertebral fractures.

PURPOSE: To investigate paraspinal muscle characteristics and lumbar bone mineral density (BMD) and their associations in routine abdominal multi-detector computed tomography (MDCT) as well as the impact of osteoporotic vertebral fractures on such associations. METHOD: 116 patients (69.7 ± 8.1 years, 72 males) who underwent routine abdominal MDCT (oncological staging and/or follow-up for tumor recurrence) were retrospectively included and assigned to a fracture and control group (age- and gender-matched), depending on the presence or absence of lumbar osteoporotic vertebral fractures. BMD was derived from lumbar vertebrae using a conversion equation, and the cross-sectional area (CSA), CSA ratio (CSA psoas muscles divided by CSA erector spinae muscles), and muscle attenuation were measured for the psoas and erector spinae muscles at the levels L2 and L4/5 without dedicated software. RESULTS: Males showed significantly higher BMD, CSA, and CSA ratios at the levels L2 and L4/5, while females had decreased erector spinae muscle attenuation at L4/5 (p < 0.05). No significant differences between patients with versus without fractures were observed except for BMD (68.5 ± 37.2 mg/ml vs. 91.4 ± 26.8 mg/ml; p < 0.01). Age-adjusted partial correlation testing revealed significant correlations of BMD and the CSA ratio at level L4/5 (r = 0.20; p = 0.03), but not with muscle attenuation (p > 0.05). CONCLUSIONS: Paraspinal muscle characteristics and lumbar BMD can be assessed seamlessly in routine abdominal MDCT without dedicated software. There are level-dependent interactions between paraspinal muscle characteristics as well as lumbar BMD. Vertebral fracture status was independent of paraspinal muscle characteristics.

Age- and gender-related variations of cervical muscle composition using chemical shift encoding-based water-fat MRI.

PURPOSE: To understand fat distribution patterns and ectopic fat deposition in healthy adults and to provide normative data, encompassing the borders of physiological regional muscle composition. For this purpose chemical shift encoding-based water-fat Magnetic Resonance Imaging (MRI) was used for proton density fat fraction (PDFF) calculations. MATERIAL AND METHODS: 91 volunteers were enrolled (male: n = 28, age = 36.6 ± 11.4 years; female: n = 63, age = 38.5 ± 15.1 years). PDFF values combined for the multifidus, semispinalis and spinalis cervicis muscles at the level of the 3rd cervical vertebral body (C3), the 5th cervical vertebral body (C5) and the first thoracic vertebral body (Th1) were extracted. RESULTS: The paraspinal musculature at C3 (14.8 ± 10.1 % vs. 19.2 ± 11.0 %; p = 0.029) and Th1 (13.8 ± 7.0 % vs 17.7 ± 7.4 %; p = 0.011) showed significantly lower PDFF values in men compared to women. Partial correlation testing with BMI as control variable revealed highly significant correlations between the paraspinal musculature PDFF at C3 (men: r = 0.504, p = 0.007; women: r = 0.279, p = 0.028), C5 (men: r = 0.450, p = 0.019; women: r = 0.347, p = 0.006) and Th1 (men: r = 0.652, p < 0.0001; women: r = 0.443, p < 0.0001) with age in both genders. CONCLUSION: The present data suggest gender and age-specific fat deposition patterns of the cervical and the upper cervicothoracic paraspinal muscles and may provide reference values for pathology detection.

Association of thigh and paraspinal muscle composition in young adults using chemical shift encoding-based water-fat MRI.

BACKGROUND: Paraspinal and thigh muscles comprise the major muscle groups of the body. We investigated the composition of the psoas, erector spinae, quadriceps femoris and hamstring muscle groups and their association to each other using chemical shift encoding-based water-fat magnetic resonance imaging (MRI) in adult volunteers. Our aim was to elucidate fat distribution patterns within these muscle groups. METHODS: Thirty volunteers [15 males, age: 30.5±4.9 years, body mass index (BMI): 27.6±2.8 kg/m2 and 15 females, age: 29.9±7.0 years, BMI: 25.8±1.4 kg/m2] were recruited for this study. A six-echo 3D spoiled gradient echo sequence was used for chemical shift encoding-based water-fat separation at the lumbar spine and bilateral thigh. Proton density fat fraction (PDFF), cross-sectional area (CSA) and contractile mass index (CMI) of the psoas, erector spinae, quadriceps femoris and hamstring muscle groups were determined bilaterally and averaged over both sides. RESULTS: CSA and CMI values calculated for the erector spinae, psoas, quadriceps and hamstring muscle groups showed significant differences between men and women (P<0.05). With regard to PDFF measurement only the erector spinae showed significant differences between men and women (9.5%±2.4% vs. 11.7%±2.8%, P=0.015). The CMI of the psoas muscle as well as the erector spinae muscle showed significant correlations with the quadriceps muscle (r=0.691, P<0.0001 and r=0.761, P<0.0001) and the hamstring group (r=0.588, P=0.001 and r=0.603, P<0.0001). CONCLUSIONS: CMI values of the erector spinae and psoas muscles were associated with those of the quadriceps femoris and hamstring musculature. These findings suggest a concordant spatial fat accumulation within the analyzed muscles in young adults and warrants further investigations in ageing and diseased muscle.

Regional variation in paraspinal muscle composition using chemical shift encoding-based water-fat MRI.

BACKGROUND: Paraspinal musculature forms one of the largest muscle compartments of the human body, but evidence for regional variation of its composition and dependency on gender or body mass index (BMI) is scarce. METHODS: This study applied six-echo chemical shift encoding-based water-fat magnetic resonance imaging (MRI) at 3 Tesla in 76 subjects (24 males and 52 females, age: 40.0±13.7 years, BMI: 25.4±5.6 kg/m2) to evaluate the proton density fat fraction (PDFF) of psoas muscles and erector spinae muscles, with the latter being divided into three segments in relation to levels of spine anatomy (L3-L5, T12-L2, and T9-T11). RESULTS: For the psoas muscles and the erector spinae muscles (L3-L5), gender differences in PDFF values were observed (PDFF psoas muscles: males: 5.1%±3.4% vs. females: 6.0%±2.2%, P=0.006; PDFF erector spinae muscles L3-L5: males: 10.7%±7.6% vs. females: 18.2%±6.8%, P<0.001). Furthermore, the PDFF of the erector spinae muscles (L3-L5) showed higher PDFF values when compared to the other segments (PDFF erector spinae muscles L3-L5 vs. T12-L2: P<0.001; PDFF erector spinae muscles L3-L5 vs. T9-T11: P<0.001) and showed to be independent of BMI, which was not the case for the other segments (T12-L2 or T9-T11) or the psoas muscles. When considering age and BMI as control variables, correlations of PDFF between segments of the erector spinae muscles remained significant for both genders. CONCLUSIONS: This study explored regional variation of paraspinal muscle composition and dependency on gender and BMI, thus offering new insights into muscle physiology. The PDFF of the erector spinae muscles (L3-L5) was independent of BMI, suggesting that this level may be suited for representative paraspinal muscle segmentation and PDFF extraction as a biomarker for muscle alterations in the future.

Acceleration of chemical shift encoding-based water fat MRI for liver proton density fat fraction and T2* mapping using compressed sensing.

OBJECTIVES: To evaluate proton density fat fraction (PDFF) and T2* measurements of the liver with combined parallel imaging (sensitivity encoding, SENSE) and compressed sensing (CS) accelerated chemical shift encoding-based water-fat separation. METHODS: Six-echo Dixon imaging was performed in the liver of 89 subjects. The first acquisition variant used acceleration based on SENSE with a total acceleration factor equal to 2.64 (acquisition labeled as SENSE). The second acquisition variant used acceleration based on a combination of CS with SENSE with a total acceleration factor equal to 4 (acquisition labeled as CS+SENSE). Acquisition times were compared between acquisitions and proton density fat fraction (PDFF) and T2*-values were measured and compared separately for each liver segment. RESULTS: Total scan duration was 14.5 sec for the SENSE accelerated image acquisition and 9.3 sec for the CS+SENSE accelerated image acquisition. PDFF and T2* values did not differ significantly between the two acquisitions (paired Mann-Whitney and paired t-test P>0.05 in all cases). CS+SENSE accelerated acquisition showed reduced motion artifacts (1.1%) compared to SENSE acquisition (12.3%). CONCLUSION: CS+SENSE accelerates liver PDFF and T2*mapping while retaining the same quantitative values as an acquisition using only SENSE and reduces motion artifacts.

Magnetic Resonance Imaging of Adipose Tissue in Metabolic Dysfunction.

BACKGROUND: Adipose tissue has become an increasingly important tissue target in medicine. It plays a central role in the storage and release of energy throughout the human body and has recently gained interest for its endocrinologic function. Magnetic resonance imaging (MRI) is an established method for quantitative direct evaluation of adipose tissue distribution, and is used increasingly as the modality of choice for metabolic phenotyping. The purpose of this review was the identification and presentation of the currently available literature on MRI of adipose tissue in metabolic dysfunction. METHOD: A PubMed (http://www.ncbi.nlm.nih.gov/pubmed) keyword search up to August 2017 without starting date limitation was performed and reference lists of relevant articles were searched. RESULTS AND CONCLUSION: MRI provides excellent tools for the evaluation of adipose tissue distribution and further characterization of the tissue. Standard as well as newly developed MRI techniques allow a risk stratification for the development of metabolic dysfunction and enable monitoring without the use of ionizing radiation or contrast material. KEY POINTS: · Different types of adipose tissue play a crucial role in various types of metabolic dysfunction.. · Magnetic resonance imaging (MRI) is an excellent tool for noninvasive adipose tissue evaluation with respect to distribution, composition and metabolic activity.. · Both standard and newly developed MRI techniques can be used for risk stratification for the development of metabolic dysfunction and allow monitoring without the use of ionizing radiation or contrast material.. CITATION FORMAT: · Franz D, Syväri J, Weidlich D et al. Magnetic Resonance Imaging of Adipose Tissue in Metabolic Dysfunction. Fortschr Röntgenstr 2018; 190: 1121 - 1130.

Gender- and Age-Related Changes in Trunk Muscle Composition Using Chemical Shift Encoding-Based Water⁻Fat MRI.

Ageing, sarcopenia, and malnutrition are associated with quantitative and qualitative changes of body composition. There are several imaging modalities, including magnetic resonance imaging (MRI), for the assessment of trunk muscle tissue composition. In this study, we investigated the gender- and age-related changes in trunk muscle composition using chemical shift encoding-based water⁻fat MRI. A total of 79 healthy volunteers (26 men: 38.9 ± 10.4 years; 53 women: 39.5 ± 15.0 years) underwent 3T axial MRI using a six-echo multi-echo 3D spoiled gradient echo sequence, allowing for the calculation of the proton density fat fraction (PDFF) in the trunk muscles. PDFF of the abdominal, psoas, and erector spinae muscles were determined. We detected significant positive correlations for abdominal muscle PDFF with age (r = 0.638, p = 0.0001) in men, and for abdominal muscle PDFF (r = 0.709, p = 0.0001) and erector spinae muscle PDFF (r = 0.674, p = 0.0001) with age in women. After adjustment for body mass index (BMI), only the correlation of age and abdominal muscle PDFF in women remained significant (r = 0.631, p = 0.0001). The findings of this study suggest that an increasing fat deposition in muscle is driven primarily by age, rather than BMI, in women. These results further support that PDFF can be considered a valid imaging biomarker of trunk muscle composition.

Anatomical Variation of Age-Related Changes in Vertebral Bone Marrow Composition Using Chemical Shift Encoding-Based Water-Fat Magnetic Resonance Imaging.

Assessment of vertebral bone marrow composition has been proposed as imaging biomarker for osteoporosis, hematopoietic, and metabolic disorders. We investigated the anatomical variation of age-related changes of vertebral proton density fat fraction (PDFF) using chemical shift encoding-based water-fat magnetic resonance imaging (MRI). 156 healthy subjects were recruited (age range 20-29 years: 12/30 males/females; 30-39: 15/9; 40-49: 4/14; 50-59: 9/27; 60-69: 5/19; 70-79: 4/8). An eight-echo 3D spoiled gradient-echo sequence at 3T MRI was used for chemical shift-encoding based water-fat separation at the lumbar spine. Vertebral bodies of L1-L4 were manually segmented to extract PDFF values at each vertebral level. PDFF averaged over L1-L4 was significantly (p < 0.05) higher in males than females in the twenties (32.0 ± 8.0 vs. 27.2 ± 6.0%) and thirties (35.3 ± 6.7 vs. 27.3 ± 6.2%). With increasing age, females showed an accelerated fatty conversion of the bone marrow compared to men with no significant (p > 0.05) mean PDFF differences in the forties (32.4 ± 8.4 vs. 34.5 ± 6.8%) and fifties (42.0 ± 6.1 vs. 40.5 ± 9.7%). The accelerated conversion process continued resulting in greater mean PDFF values in females than males in the sixties (40.2 ± 6.9 vs. 48.8 ± 7.7%; p = 0.033) and seventies (43.9 ± 7.6 vs. 50.5 ± 8.2%; p = 0.208), though the latter did not reach statistical significance. Relative age-related PDFF change from the twenties to the seventies increased from 16.7% (L1) to 51.4% (L4) in males and 76.8% (L1) to 85.7% (L4) in females. An accelerated fatty conversion of bone marrow was observed in females with increasing age particularly evident after menopause. Relative age-related PDFF changes showed an anatomical variation with most pronounced changes at lower lumbar vertebral levels in both sexes.

Associations Between Lumbar Vertebral Bone Marrow and Paraspinal Muscle Fat Compositions-An Investigation by Chemical Shift Encoding-Based Water-Fat MRI.

Purpose: Advanced magnetic resonance imaging (MRI) methods enable non-invasive quantification of body fat situated in different compartments. At the level of the lumbar spine, the paraspinal musculature is the compartment spatially and functionally closely related to the vertebral column, and both vertebral bone marrow fat (BMF) and paraspinal musculature fat contents have independently shown to be altered in various metabolic and degenerative diseases. However, despite their close relationships, potential correlations between fat compositions of these compartments remain largely unclear. Materials and Methods: Thirty-nine female subjects (38.5% premenopausal women, 29.9 ± 7.1 years; 61.5% postmenopausal women, 63.2 ± 6.3 years) underwent MRI at 3T of the lumbar spine using axially- and sagittally-prescribed gradient echo sequences for chemical shift encoding-based water-fat separation. The erector spinae muscles and vertebral bodies of L1-L5 were segmented to determine the proton density fat fraction (PDFF) of the paraspinal and vertebral bone marrow compartments. Correlations were calculated between the PDFF of the paraspinal muscle and bone marrow compartments. Results: The average PDFF of the paraspinal muscle and bone marrow compartments were significantly lower in premenopausal women when compared to postmenopausal women (11.6 ± 2.9% vs. 24.6 ± 7.1% & 28.8 ± 8.3% vs. 47.2 ± 8.5%; p < 0.001 for both comparisons). In premenopausal women, no significant correlation was found between the PDFF of the erector spinae muscles and the PDFF of the bone marrow of lumbar vertebral bodies (p = 0.907). In contrast, a significant correlation was shown in postmenopausal women (r = 0.457, p = 0.025). Significance was preserved after inclusion of age and body mass index (BMI) as control variables (r = 0.472, p = 0.027). Conclusion: This study revealed significant correlations between the PDFF of paraspinal and vertebral bone marrow compartments in postmenopausal women. The PDFF of the paraspinal and vertebral bone marrow compartments and their correlations might potentially serve as biomarkers; however, future studies including more subjects are required to evaluate distinct clinical value and reliability. Future studies should also follow up our findings in patients suffering from metabolic and degenerative diseases to clarify how these correlations change in the course of such diseases.

Non-invasive Measurement of Brown Fat Metabolism Based on Optoacoustic Imaging of Hemoglobin Gradients.

Metabolism is a fundamental process of life. However, non-invasive measurement of local tissue metabolism is limited today by a deficiency in adequate tools for in vivo observations. We designed a multi-modular platform that explored the relation between local tissue oxygen consumption, determined by label-free optoacoustic measurements of hemoglobin, and concurrent indirect calorimetry obtained during metabolic activation of brown adipose tissue (BAT). By studying mice and humans, we show how video-rate handheld multi-spectral optoacoustic tomography (MSOT) in the 700-970 nm spectral range enables non-invasive imaging of BAT activation, consistent with positron emission tomography findings. Moreover, we observe BAT composition differences between healthy and diabetic tissues. The study consolidates hemoglobin as a principal label-free biomarker for longitudinal non-invasive imaging of BAT morphology and bioenergetics in situ. We also resolve water and fat components in volunteers, and contrast MSOT readouts with magnetic resonance imaging data.

MR-based assessment of body fat distribution and characteristics.

The assessment of body fat distribution and characteristics using magnetic resonance (MR) methods has recently gained significant attention as it further extends our pathophysiological understanding of diseases including obesity, metabolic syndrome, or type 2 diabetes mellitus, and allows more detailed insights into treatment response and effects of lifestyle interventions. Therefore, the purpose of this study was to review the current literature on MR-based assessment of body fat distribution and characteristics. PubMed search was performed to identify relevant studies on the assessment of body fat distribution and characteristics using MR methods. T1-, T2-weighted MR Imaging (MRI), Magnetic Resonance Spectroscopy (MRS), and chemical shift-encoding based water-fat MRI have been successfully used for the assessment of body fat distribution and characteristics. The relationship of insulin resistance and serum lipids with abdominal adipose tissue (i.e. subcutaneous and visceral adipose tissue), liver, muscle, and bone marrow fat content have been extensively investigated and may help to understand the underlying pathophysiological mechanisms and the multifaceted obese phenotype. MR methods have also been used to monitor changes of body fat distribution and characteristics after interventions (e.g. diet or physical activity) and revealed distinct, adipose tissue-specific properties. Lastly, chemical shift-encoding based water-fat MRI can detect brown adipose tissue which is currently the focus of intense research as a potential treatment target for obesity. In conclusion, MR methods reliably allow the assessment of body fat distribution and characteristics. Irrespective of the promising findings based on these MR methods the clinical usefulness remains to be established.

Discrimination Between Brown and White Adipose Tissue Using a 2-Point Dixon Water-Fat Separation Method in Simultaneous PET/MRI.

UNLABELLED: The purpose of the study was to evaluate signal-fat-fraction (SFF) analysis based on a 2-point-Dixon water-fat separation method in whole-body simultaneous PET/MR imaging for identifying brown adipose tissue (BAT) and discriminating it from white adipose tissue (WAT) using cross-validation via PET. METHODS: This retrospective, internal review board-approved study evaluated 66 PET/MR imaging examinations of 33 pediatric patients (mean age, 14.7 y; range, 7.4-21.4 y). Eleven elderly patients were evaluated as controls (mean age, 79.9 y; range, 76.3-88.6 y). Pediatric patients were divided into 2 groups: with and without metabolically active supraclavicular BAT. The standard of reference for the presence of BAT was at least 1 PET examination showing (18)F-FDG uptake. PET/MR imaging included a 2-point Dixon water-fat separation method. Signal intensities in regions of interest on fat and water images and mean standardized uptake values (SUVmean) were determined bilaterally in supraclavicular and gluteal fat depots. SFF was calculated from the ratio of fat signal over summed water and fat signal. Statistical analysis was conducted using the Student t test and correlation analysis. RESULTS: SFF was significantly lower (P < 0.0001) in supraclavicular BAT than gluteal WAT in all pediatric subjects. Supraclavicular SFF was significantly higher in the control than in the pediatric group (P < 0.0001). In PET-positive patients with multiple examinations, SFF stayed stable whereas SUVmean fluctuated (median intraindividual change, 5% vs. 91%). No significant correlation between SUVmean and SFF could be observed for BAT. CONCLUSION: The results demonstrate that MR imaging-SFF analysis is a reproducible imaging modality for the detection of human BAT and discrimination from WAT. SFF values of BAT are independent from its metabolic activity, making SFF a more reliable parameter for BAT than the commonly used PET signal. However, with the intent to investigate both the composition of BAT and its activation status, hybrid PET/MR imaging might provide supplemental information.